<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>id选择器</title>
		<style>
			#blue {
				width: 400px;
				height: 100px;
				background-color: blue;
			}
			#green {
				width: 400px;
				height: 100px;
				background-color: green;
			}
			#blue2 {
				width: 400px;
				height: 100px;
				background-color: red;
			}
		</style>
	</head>
	<body>
		<div id="blue"></div>
		<div id="green"></div>
		<div id="blue2"></div>
	</body>
</html>